Operator Precedence & Associativity in C

What is Operator Precedence?

Operator Precedence means the priority level of operators. Operators with higher precedence execute before those with lower precedence.

What is Associativity?

Associativity tells whether an expression is evaluated **left-to-right** or **right-to-left** when multiple operators have the same precedence.

Operator Precedence Table

Highest → Lowest Precedence

1.  ++  --  (unary), !, ~, sizeof
2.  *   /   %
3.  +   -
4.  <<  >>
5.  <   <=   >   >=
6.  ==  !=
7.  &
8.  ^
9.  |
10. &&
11. ||
12. ?:    (ternary)
13. =, +=, -=, *=, etc.
14. ,

(This is simplified for beginner clarity.)

Associativity Rules

Left-to-Right Associativity:
+ -  * / %  < > <= >=  == !=  && ||

Right-to-Left Associativity:
=  +=  -=  *=  /=  
!  ~  ++  --  sizeof  
?:   (ternary)

Example 1 – Precedence of *, +

#include <stdio.h>

int main() {

    int result = 10 + 20 * 3;

    // 20 * 3 = 60
    // 10 + 60 = 70

    printf("Result = %d", result);

    return 0;
}

Example 2 – Parentheses Change Precedence

#include <stdio.h>

int main() {

    int a = (10 + 20) * 3;

    // 10 + 20 = 30
    // 30 * 3 = 90

    printf("a = %d", a);

    return 0;
}

Example 3 – Pre/Post Increment & Multiplication

#include <stdio.h>

int main() {

    int a = 5;
    int result = ++a * 3;

    // ++a happens first → a = 6
    // 6 * 3 = 18

    printf("Result = %d", result);

    return 0;
}

Example 4 – Left-to-Right Associativity

#include <stdio.h>

int main() {

    int x = 20 - 5 - 3;

    // (20 - 5) = 15
    // (15 - 3) = 12

    printf("x = %d", x);

    return 0;
}

Example 5 – Right-to-Left Associativity

#include <stdio.h>

int main() {

    int a;
    a = 5 + 3 * 2;

    printf("a = %d\n", a);

    int b;
    b = a = 20;

    printf("b = %d", b);

    return 0;
}

Example 6 – Complex Expression Evaluation

#include <stdio.h>

int main() {

    int a = 5, b = 10, c = 2;

    int result = a + b * c - ++a;

    // Step 1: ++a → a becomes 6
    // Step 2: b * c = 20
    // Step 3: a + (b*c) - new a → 5 + 20 - 6 = 19

    printf("Result = %d", result);

    return 0;
}

Diagram – How Precedence Works

Expression:  5 + 3 * 2

   * (multiplication)
       |
       v
5 + (3 * 2)
       |
       v
     5 + 6
       |
       v
       11

Practice Questions

1. Define operator precedence and associativity.
2. Why are parentheses important in expressions?
3. Evaluate: 12 + 6 / 3 * 2
4. Evaluate: 10 - 5 - 2 (explain associativity)
5. Write a program that shows precedence of ++ and *

Practice Task